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"These outrageous allegations are simply false," he said in his statement. "I have been transparent and truthful about these vile claims, but I will not further engage publicly with a coordinated smear campaign."

Porter resigned over the objections of White House chief of staff John Kelly and others, a White House official said.

"Rob Porter is a man of true integrity and honor and I can't say enough good things about him. He is a friend, a confidante and a trusted professional. I am proud to serve alongside him," Kelly said in a statement.

The allegations were first reported by the Daily Mail earlier this week.

Porter has been dating White House communications director Hope Hicks, one of the most influential figures in the West Wing, several people familiar with their relationship say. Hicks was involved in crafting Porter's response to the allegations of domestic abuse being leveled against him.

His last day at the White House has not yet been set, according to White House press secretary Sarah Sanders, who added that Porter will stay on to ensure a smooth transition to his successor.

Porter, a graduate of Harvard Law School and a Rhodes scholar, previously worked for Republican Sens. Orrin Hatch, Rob Portman and Mike Lee.

Hatch issued a statement strongly supporting Porter, his former chief of staff, on Tuesday, calling the reports a "vile attack" and a "cynical campaign to discredit his character."But following Porter's resignation and new reporting on abuse allegations, Hatch issued a new statement Wednesday. An aide to the senator told CNN that the original Tuesday statement, which the White House sent to reporters on Wednesday along with other statements of support for Porter, no longer applied.

"I am heartbroken by today's allegations. In every interaction I've had with Rob, he has been courteous, professional and respectful. My staff loved him and he was a trusted adviser. I do not know the details of Rob's personal life. Domestic violence in any form is abhorrent. I am praying for Rob and those involved," Hatch said.

A former chief of staff to Hatch, Porter joined the White House at the beginning of Trump's administration, though he wasn't well-known to the President like other top West Wing staffers.

As staff secretary, Porter's responsibility was mainly in the flow of paper that crossed Trump's desk, including the wave of executive orders and actions that Trump inked during the first months of his tenure. A lawyer, Porter also participated in the process of legal vetting the myriad documents that require the President's signature.

Porter's role was under-the-radar, and Trump himself remained largely unfamiliar with him for weeks before his role was explained. The President was impressed by Porter's educational credentials -- including degrees from Harvard and Oxford -- a person familiar with the matter said.

When Kelly replaced Reince Priebus as White House chief of staff, Porter's role expanded. Kelly imposed a strict system of information flow to the President, elevating the importance of Porter's task in managing the documents, news clippings and briefing books that entered the Oval Office.

He was also seen as a neutral arbiter between warring West Wing factions, helping bridge gaps between those who worked on Trump's campaign and the faction of aides who came from other Republican circles. Kelly in particular viewed Porter as a right-hand man who would impose his system of order even in his absence.

Porter began traveling more frequently in Trump's entourage, including last month's trip to the World Economic Forum in Davos. Kelly himself remained behind in Washington, as did the top policy adviser Stephen Miller.

A person familiar with West Wing dynamics said Porter has expressed interest in an elevated policy role over the past weeks. He's been approached by private sector firms over the past several months with offers to leave the administration, and has considered them, but told colleagues earlier this year that he wasn't planning on leaving the White House, the person said.

White House staff secretaries play an important role in the West Wing, though the position has varied in stature. Under President Barack Obama, the role was downgraded to a "deputy assistant to the president" title. Trump restored the job as an "assistant to the president."